GUWAHATI, Feb 6 - Excessive use of chemical fertilizers and pesticides in the tilling fields and the tea estates in their vicinity may lead to fluoride and arsenic contamination of the surface water available in the ponds and the ground water accessed through hand pumps in the localities, besides damaging the soil condition to a great extent.
The findings of a study carried out by the city-based private sector laboratory Neoland Technology, under the sponsorship of the Assam Science Technology and Environment Council (ASTEC) in five development blocks in five different districts of the State, have led to the above conclusion.
Talking to this correspondent, Dr DN Chakravorty of the Neoland Technology said the study was carried out in 2013 at the five development blocks of Besimary in Darrang district, Moirabari in Morigaon district, Dimoria in Kamrup (Metro) district, Titabor in Jorhat district and Lahowal in Dibrugarh district.
Though the levels of the fluoride and arsenic contamination of the water of the ponds and the hand pumps were found to be below the toxic limit in these development blocks, the findings underlined the need to follow the scientific norms for applying chemical fertilizers and pesticides in the tilling fields and the tea estates, Chakravorty, also a former Dean of the Assam Agricultural University (AAU), said.
He informed that the analysis of the fertiliser residue in soils reveal that the pH value of the soils mostly varied from medium to very strongly acidic in reaction, which are somewhat lower than the district data.
These values (5.42 to 7.69) are lower than the values analysed in the same areas 10 years back in 2003 for a similar project. One reason for the change may be due to continuous use of chemical fertilizers in these areas and leaching of the soil base materials due to heavy rains, he said.
It needs mention here that the pH scale measures how acidic or basic a substance is. It ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is alkaline. Each whole pH value below 7 is ten times more acidic than the next higher value.
The soil electrical conductivity (EC) values of the soils of these districts were also found to be very low and they vary between 8.32 Micro Mohs (�mhos) per cm in Nagaon to 732.20 �mhos per cm in Barpeta district. This indicates that most of the soils are non-saline in nature, he said. The soil EC is a means to measure the salinity of soil.
Similarly the variation in calcium (Ca) content in the soils of the districts are 8.02 parts per million (ppm) to 56 ppm in Barpeta, 0 to 24.05 ppm in Darrang, 16.03 ppm to 84.17 ppm in Kamrup and 36.07 ppm to 64.13 ppm in Nagaon. These figures are lower than the earlier ones found in the 2003 study, indicating that the Ca content of the soils was decreasing during the last 10 years, said Dr Chakravorty.
It is worth mentioning here that the high calcium value in soils helps correct soil acidity, improves soil structure, thus the soil overcomes the harmful or toxic effects of excess soluble salts of magnesium, sodium and potassium, providing proper conditions for microbiological growth and regulating nutrient absorption into the plants.